Induction furnace



Nov. 8, 192 7.

J. M. WEED INDUCTION FURNACE Filed Dec.- 14. 1923 2 Sheets-Sheet 1 Fig. 2.

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Nov. 8, 1927.

J. M. WEED INDUCTION FURNACE Filed Dec. 14. 1925 2 Sheets-Sheet 2 Fig. 5.

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Inventor James TT]. Weed,

His Attovneg.

Patented Nov. 8, 1927,

UNITED STATES PATENT OFFICE.

JAMES M. WEED, 0F SCOTIA, NEW YORK, ASSIGNOB TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

INDUCTION FURNACE.

Application filed December 14, 1923. Serial No. 880,716.

My invention relates to electric induction furnaces and has for its object the provision of an improved furnace construction whereby a more effective circulation of molten charge may be produced.

More specifically, my invention relates that type of electric induction furnaces m which the crucible provides a reservoir and communicating therewith a looped cavity or chamber in which a portion of the charge is heated by secondary currents, the portion of the charge in said chamber constituting a closed secondary for the primary wlnding. In such furnaces, for uniform and effective heating of the charge, the charge must be caused to circulate between the secondary chamber and the reservoir. It is particularly im ortant that all of the charge in the secondhry should circulate activel as otherwise the metal may be overheated 1n the stagnant spots.

In my co-pending application, Serial No. 525,660, filed December 29, 1921, relating to furnaces of this type, I have described and claimed a method of producing circulation of charge by so disposing the primary WlIld ing with relation to the secondary chamber that differences in fluid pressure are produced in opposite ends or boundaries of said chamber, ducts or channels being provided between the respective ends of the chamber and the reservoir through which the charge can flow. In carrying out my present invention I utilized the same general method of producing circulation, mv present invention relating more particularly to an improved construction of furnace crucible whereby the circulation is directed so as to assure a more complete and uniform movement of the charge and hence the elimination of stagnant spots. In one form of my invention, the charge is given a rotating or spiral motion so as to circulate in both an axial and a circumferential direction through the secondary cylinder.

For a more complete understanding of my invention reference should be made to the accompanying drawings, in which Fig. 1 is a vertical section taken alon the line 1-1 of Fig. 3, looking in the direction of the arrows;

Fig. 2 is a vertical section taken along the.

line 22 of Fig. 3, lookin in the direction of the arrows; Fig. 3 is a orizontal section of an electric induction furnace embodyingmy invention; Fig. 4 is a vertical section showing while igs. 5 6, and 7 are views showing another modification of my invention,

Referring to Figs. '1, 2, and 3, of the drawmg, I have shown my invention in one form as apphed to an induction furnace having a cruclble 10 comprising a reservoir 11 for the charge and a cylindrical cavity 12 in which a portion of the charge constltutes a closed secondary communicating with the reservoir 11 through ducts 13 and 14. Heating currents are induced in the secondary portion of the charge by means of a primary winding 15, both primary and secondary being linked in common with a laminated iron core 16. As shown, the primary and secondary are concentrically arranged, the primary being located inside the secondary, and the primary is displaced in an axial direction with respect to the secondary with the result that unequal fluid pressures are produced at opposite ends of the secondary cylinder due to electromagnetic repulsion between the primary and secondary, as described and claimed in my aforesaid copending application. This action may be briefly explained as follows.

Since the axial displacement of the primary winding is in this case toward the left, the force of repulsion is in a direction tending to move the secondar toward the right, as viewed in Fig. 2. The secondar as a whole is not free to move, but considering the various current carrying elements from left to right, it should be noted that the forces or pressures are cumulative toward the right and end of the secondary cylinder since the pressure applied to any element of the fluid will be transmitted to the succeeding elements in the direction of its application. This results in an increased fluid pressure 'at the end of the secondary most remote from the primary; i. e., at the right hand end as viewed in Fig. 2. A circulation of charge is therefore produced from the secondary to the reservoir through duct 14 and from the reservoir back to the secondary through duct 13,

a modified form of my invention,

this circulation being from the region of high fluid pressure in the secondary to the reservoir and from the reservoir to the region of low ressure in the secondary. Obviously, by displacing the primary in the opposite direction, the direction of flow can be reversed.

In my aforesaid co-pending application, the points of communication between the secondary and the reservoir are situated in a common plane passing through the axis of the secondar In that case the principal direction of circulation of the charge through the secondary is axial, the stream of molten charge entering through the duct at one end of the cylinder and leaving through the duct at the opposite end. Combined with this flow in an axial direction is the circumferential distribution of the charge at the incoming end of the cylinder and its circumferential collection at the outgoing end. This circumferential flow is in both directions from the mouths of the ducts, the maximum circumferential travel being only 180.

Under these conditions the side of the secondary cylinder opposite from the mouths of the ducts will be a relatively stagnant region.

My present invention consists in an arrangement of the ducts of communication between the secondary cylinder and the reservoir such that a rotating or spiral motion is imparted to the charge in its passage through the secondary cylinder, and this stagnant region thus eliminated. The

' charge in its passage through the secondary has a circumferential as well as an axial direction of flow. As shown in Figs. 1, 2, and 3, the ducts 13 and let leading from the reservoir to the secondary are displaced circumferentially with respect to the secondary, as well as being axially displaced so as to communicate with the ends of the secondary cylinder. The charge as it flows from the reservoir through duct 13 is directed by the duct substantially tangentially with respectto the circumference of the secondary. After the charge enters the secondary it has a tendency due to its inertia to continue its flow in the direction in which it enters, and therefore the charge flows in a counter clockwise direction as viewed in Fig. 1 around the secondary. This circumferential motion of the charge in the secondary, in addition to its axial motion, is further accentuated by the fact that duct 14 is also substantially tangential with respect to the secondary and extends in a direction to freely discharge the spiral stream of molten charge.

In the manner described above I have provided for active and uniform circulation of the charge in the secondary c linder, the spiral motion imparted to the c arge assuring that all portions are kept in motion so that there are no stagnant s ots. The charge is thus maintained at a substantially uniform temperature and the heat generated in the secondary is utilized with the greatest possible efliciency.

In the modified form of my invention shown in Fig. 4, the ducts 17 and 18 extend in more truly tangential directions with relation to the circumference of the secondary. Also, the reservoir 20 is circular cylindrical in shape at the bottom so that the directions of the ducts are tangential with respect to the inner walls of the reservoir at the points of communication therewith. This construction ofiers the least possible resistance to flow of charge and therefore facilitates its passage into and through the secondary. It also favors a rotating or rolling motion of the molten charge in the reservoir.

In the particular form shown in Figs. 1 to 23 inclusive, the furnace crucible is made in sections which may be preformed and afterwards assembled, a suitable cement being used at the joints. The crucible comprises an upper section 21 which is substantially cylindrical and forms the side Walls of the reservoir. The bottom of the reservoir is formed by an extension 23 on the wall of a cylindrical section 22, which extension fits into the lower end of section 21. Section 22 forms also the outer wall of the secondary cylinder. Concentric with the section 22 and inside thereof is cylindrical section 24, forming the inner wall of the secondary. The construction of the crucible of the modified form shown in Fig. 4 is similar to that described for Figs. 1, 2, and 3, the shape being changed somewhat as previously noted. The crucible is preferably surrounded by a layer 21 of suitable heat insulating material, and an outer shell 21 of steel so arranged as to avoid a conductive circuit about the core in which a secondary current might be induced.

In the modified form of my invention shown in Figs. 5, 6,and 7, the crucible section 22 is provided with an enlarged opening 25 connecting the secondary cylinder 12 with the reservoir 11. This opening embraces the area within which the communicating ducts between the secondary and the reservoir may be desired. Into the opening 25, a .block 26 (Fig. 6) is fitted. This block is provided with rooves or channels 27 and 28 at its ends, w iich channels form ducts connecting the secondary and reservoir when the lock is fitted in place, as shown in Fig. 5. As shown, the channels 27 and 28 are arranged so as to form ducts which are truly tangential like those shown in Fig. 4.

ducts. The arrangement ofthe ducts may be varied to give any desired form, as that shown in Figs. 1, 2, and 3, that of Fig. 4, or that of the aforementioned previous patent application by inserting a suitable block similar to 26. The block 26 may also be omitted entirely if desired as shown in thereof will suggest themselves to those skilled in the art Without departing from the spirit of my invention, the scope of which is set forth in the annexed claims.

lVhat I claim as new and desire to secure by Letters Patent of the United States, is 2- 1. An induction furnace comprising a crucible providing a reservior for the charge and a looped chamber communicating with said reservoir Within which a portion of the charge constitutes a closed secondary, a primary winding for inducing heating currents in said secondary, and means for causing said charge to flow in a substantially spiral path through, said chamber, the return flow being through said reservoir.

2. In an induction furnace, a crucible providing a reservoir for the charge and a substantially cylindrical chamber communicating therewith within which a portion of the charge constitutes a closed secondary, a primary winding for inducing heating currents in said secondary, means for producing a flow of charge in a general axial direction through said chamber, and means for giving the charge a circumferential component of flow in its passage through said chamber.

0 3. An induction furnace comprising a crucible providing a reservoir for the charge and communicating with said reservoir a chamber bounded by inner and outer cylindrical surfaces within which a portion of the charge constitutes a closed secondary, a primary winding for inducing heating currents in said secondary, and means for producing a flow of charge through said chamber in ,a general axial direction with return flow through said reservoir, the passages of communication between said chamber and said reservoir being arranged to give the charge a circumferential component of flow in its passage through said chamber.

4. An induction furnace comprising a crucible providinr a. reservoir for the charge and a cylindrical chamber within which a portion of the charge constitutes a closed secondary, said crucible being provided with ducts leading from said reservoir to circumferentially and axially displaced points of said chamber, and a primary winding for inducing an electric heating current in said secondary, said primary winding being axially displaced with relation to said chamber whereby a flow of charge is produced in a spiral direction through said chamber. the return flow being through said reservoir.

5. An induction furnace comprising a crucible providing a reservoir for the charge and a cylindrical chamber communicatin with said reservoir through ducts tangentia to said chamber in which a portion of the charge constitutes a closed secondary, a primary winding for inducing an electric heating current in said secondary, and means for producing a flow of charge through said chamber in an axial direction with return flow through said reservoir, thecharge being directed by said ducts in a circumferential direction within said chamber.

6. An induction furnace comprising a crucible providing a reservoir for the charge and a looped chamber in which a portion of the charge constitutes a closed secondary, said crucible providing ducts leading from said reservoir to said chamber at opposite boundaries thereof and in directions tangential thereto, and a primary winding for inducing an electric heating current in said secondary, said primary winding being displaced with relation to said secondary so as to produce a flow of charge through said chamber from one side to the other and return flow through said reservoir, the charge being directed circumferentially by said ducts in its passage through said chamber.

7. An electric furnace comprising a crucible providing a plurality of chambers for the charge communicating with each other through an aperature, a member fitting in said aperature formed to provide ducts connecting said chambers at separate points, and electric means for heating the charge in one of said chambers.

8. An electric furnace comprisin a crucible forming a reservoir for the c arge, a looped chamber, and an aperture connecting said reservoir and chamber, a refractory member fitting in said aperture formed to provide ducts connecting said chamber and reservoir at separate .points, means for producing electric heating currents in a portion of the charge in said loop chamber, and means. for producing a flow of charge through said ducts between said chamber and reservoir.

9. An electric furnace comprising a crucible providing a plurality of chambers communicating with each other through an aperture, a removable member fitting in said aperture providing ducts connecting said chambers at separate points, and electrical means for heating a portion of the charge in one of said chambers.

10. An electric furnace comprising a fur-- nace crucible providinga reservoir for the charge and a-looped chamber communicating with said reservoir through an aperature, a removable refractory member fitting in said aperture provided with ducts connecting said chamber and reservoir at separate points, means for inducing electric heating currents in a portion of the charge in said looped chamber, and means for producing a flow of charge through said ducts between said chamber and reservoir.

11. An electric furnace comprising acrucible providing a reservoir for the charge and an annular chamber communicating at one side with said reservoir through an aperture, a removable refractory member fitting in said aperture providin channels connecting said reservoir and c iamber at separate points, a primary winding for inducing an electric heating current in a portion of the char e in said annular chamber, said primary win ing being displaced with relation to said chamber so as to produce a flow of charge from said chamber to said reservoir through one of said channels, the charge returning from the reservoir to the chamber through the other channel.

In witness whereof, I have hereunto set my hand this 13th day of December 1923.

JAMES M. WEED. 

